The invention relates to a vapor barrier, which is arranged facing the room, for use in the thermal insulation of buildings, especially for thermal insulation procedures in new buildings and in the renovation of old buildings.
In order to reduce the carbon dioxide emission which occurs as a result of heating buildings, thermal insulation procedures are carried out in the construction of new buildings and in the renovation of old buildings. For economic reasons, which constantly have to be considered by the owner of the building, the question of cost also has to be taken into account here. Moreover, the external appearance of the building is a significant factor here which also represents a limit to what can actually be done. Thus, for example, thermal insulation procedures of this kind can be carried out only in buildings, which have a visible framework, by means of insulation layers which are located internally. An acceptable amount of moisture in the framework wood must also be ensured, especially under winter conditions, via the possible diffusion of vapor and also by the vapor barrier facing the room. In contrast to this, the moisture, which is due to rain and which penetrates through the joints between the wooden posts and the nogging, must also be able to dry out toward the inside in the summer months in order to ensure long life for the wood that is used in the framework despite the improved thermal insulation characteristics.
Similar difficulties also arise in subsequent full-rafter insulation on high-pitched roofs with a vapor-tight front covering, for example, roofing fabric on planking. Thus tests carried out by the Fraunhofer Institut für Bauphysik in the case where vapor barriers were applied inside with a water vapor diffusion resistance (sd value) which is less than a 10 m diffusion-equivalent air layer thickness, especially on roofs oriented toward the north, showed that the extent to which the planking dries out in the summer is not sufficient to achieve a wood moisture situation which is harmless. Thus vapor barriers which are applied facing the room can no longer adequately carry away moisture accumulations which are caused by convection, for example.
Proceeding from these known disadvantages, the problem for the invention is to create a vapor barrier which is arranged facing the room and which is capable—under different ambient conditions which are variable in use—of ensuring water vapor exchange between the room air and the interior of the building component which will, as extensively as possible, prevent damage by moisture to the building material that is used.